Effects of bentonite, diatomite and metakaolin on the rheological behavior of 3D printed magnesium potassium phosphate cement composites

Abstract

In this study, the effects of bentonite, diatomite, and metakaolin on the rheological behavior of 3D printed magnesium potassium phosphate cement composites (3D printed MKPCs) were investigated through characterization of the material properties, including yield stress, plastic viscosity, thixotropy, and creep. The thixotropy was studied by assessing the hysteresis area and thixotropic parameters under dynamic shear tests. The structural stability was evaluated by assessing the creep recovery, modulus of the fresh cement pastes, and deformation rate of the printed specimens. The results showed that diatomite played a key role in enhancing the thixotropy of the 3D printed MKPCs. Bentonite was found to significantly enhance the static yield stress, creep resistance, and shape stability owing to its high water absorption in the 3D printed MKPCs. Isothermal calorimetry testing showed that all additives accelerated the hydration reaction, which was confirmed by the increased compressive strength. Finally, a schematic representation of the yield stress evolution with time was proposed, revealing the beneficial effects of three additives in MKPCs during different stages of 3D printing.